Plan B
Meaning of Plan B: Timing decides whether it can work at all, because the drug acts on the release of an egg and not on anything afterward.
Definition of Plan B
Plan B is a brand of emergency contraceptive containing levonorgestrel, a synthetic progestin. It is taken as a single dose after unprotected sex or the failure of another method, and it lowers the chance of pregnancy mainly by delaying or preventing the release of an egg from the ovary. It is sold without a prescription.
How does it work?
Release of an egg is triggered by a surge of luteinizing hormone from the pituitary gland. Levonorgestrel suppresses or delays that surge, so ovulation is postponed past the window in which sperm already present remain able to fertilize. That is the whole of its established mechanism. Once an egg has been released, the drug has little to offer, which is why effectiveness depends heavily on where a person is in the cycle and on how soon it is taken.
Two things it does not do are worth stating plainly. It does not end an established pregnancy, and it is not the same medicine as the drugs used for that purpose. Current evidence also does not support the idea that it works by preventing a fertilized egg from implanting.
How does it compare with other emergency options?
| Option | How it works | Points of difference |
|---|---|---|
| Levonorgestrel tablet, including Plan B and other brands | Delays or prevents ovulation | Available without prescription; effectiveness falls the longer it is left |
| Ulipristal acetate tablet | Blocks the hormone signal closer to the point of ovulation | Prescription only in many places; remains effective later in the window |
| Copper intrauterine device | Copper ions make the uterus and tubes hostile to sperm and eggs | The most effective emergency method, and it continues as ongoing contraception |
How is it different from a regular birth control pill?
The active ingredient overlaps: levonorgestrel is the progestin in several ordinary contraceptives. The difference is the amount and the pattern. A daily birth control pill holds ovulation suppressed continuously through steady low doses, while emergency contraception is a single larger dose intended to interrupt one cycle. It is less reliable than a method used consistently, and it offers no protection against sexually transmitted infection. Nausea, irregular bleeding and a shift in the timing of the next period are the effects most often reported afterward.
Also known as
Used in a sentence
The patient asked about emergency contraception options, including Plan B, after a barrier method failure.
Good to know
Emergency contraception containing levonorgestrel prevents or delays ovulation and is distinct from medications used to end an existing pregnancy, a common point of confusion between the two.